1. Field
The following disclosure relates to an input system and a method for detecting touch using the same, more particularly, to an input system that is able to realize a stylus pen with no battery in a display device and to detect touch using a human finger or a stylus pen, and a method for detecting touch using the same.
2. Background
As the world officially entered the information technology era, techniques for a display device configured to present an electrical information signal into a visual image have grown rapidly. To meet the demands of the rapidly growing display techniques, various types of flat display devices with desirable features have been developed which can be substituted for conventional cathode ray tube (CRT) devices. Such features include small thickness, light weight, and low power consumption.
Typical examples of such a flat panel display device include a liquid crystal display device (LCD), a plasma display panel device (PDP), a field emission display device (FED), an electro luminescence display device (ELD), and the like. Those examples commonly include a flat display panel configured to realize an image as an essential component. Such a flat display panel has a structure in that an optical anisotropic film or a luminance film is disposed between a pair of transparent insulator substrates bonded oppositely.
Such a display device having the above-mentioned structure increasingly requires a touch panel that can recognize a touch position via human fingers or auxiliary input means to transmit corresponding information to meet the recognized touch position. Currently, such a touch panel is applied as an attach-type panel attached to an outer surface of the display device.
According to a touch detecting method, the touch panel is classified into a resistance type, a capacitance type, and infrared ray detecting type. In view of the manufacture system convenience and the sensing ability, the capacitance type touch panel has been receiving more attention recently.
Mobile devices, such as a smart phone, a smart book, and the like, have become more popular as HIDs (Human Interface Devices) using a human finger or using a stylus pen that enables writing or drawing as an input device. A stylus pen input enables more detailed input and gives advantages of detailed drawing and writing.
A capacitance-type touch screen in a related art will be described as follows, with reference to the accompanying drawings.
FIG. 1 is a circuit diagram of a capacitance-type touch detecting circuit in a related art. FIG. 2 is a graph of voltage output based on the time divided according to presence of a finger touch using the circuit diagram of FIG. 1.
As shown in FIG. 1, a capacitance-type touch detecting circuit includes a first electrode (Tx) and a second electrode (Rx), an amplifier 5 receiving a reference voltage (Vref) via a (+) input terminal, and a capacitor (Cs) formed between an output terminal of the amplifier 5 and an (−) input terminal.
In this instance, the first electrode (Tx) receives an input voltage (Vin) via a pad provided in an end thereof and senses an output voltage (Vout) output from the amplifier 5 via a pad provided in an end of the second electrode (Rx).
A square wave of typically 2-3 μs is used as a touch driving signal and applied to the first electrode (Tx). A voltage value in proportion to a value of mutual capacitance variation (ΔCm) between the first and second electrodes (Tx and Rx) is sensed as the output voltage (Vout).
As time passes after the square wave is applied as an input voltage as shown in FIG. 2, the output voltage (Vout) is increased in case of finger touch. When there is a finger touch, a finger contacts with the electrode, and the mutual capacitance variation (ΔCm) decreases. Accordingly, the rate of increase of the output voltage (Vout) is decreased (as in the dotted line in FIG. 2), and such decrease is calculated at a cross section between each Tx channel and each Rx channel. Coordinates of the finger touch can be extracted from such data.
However, when the touch detecting circuit of FIG. 1 is used in stylus pen touch as well as finger touch, a contact area of a sensor panel face positioned in a top of a stylus pen is relatively small and it is difficult to sense mutual capacitance variation in touch implemented by the stylus pen, because mutual capacitance Cm between electrodes is small. Accordingly, the accuracy of coordinate extraction might be deteriorated.
Moreover, when a tip of the stylus pen is smaller than the electrode provided in a sensor panel for sensing, coordinate distortion could be generated thereby affecting the sensitivity of the sensor directly.
When the finger touch and the stylus pen touch use the same touch detecting circuit, one disadvantage is that touch implemented by the palm in contact with the electrode in the stylus pen input cannot be distinguished from the touch implemented by the stylus pen. In other words, in the detecting circuit shown in FIG. 1, it is difficult to have palm rejection in the stylus pen touch module.
Another driving module for detecting touch by another driving module, for instance, an electromagnetic driving module different from the stylus pen touch or finger touch is introduced. In this instance, an auxiliary panel that can be detected by an auxiliary electromagnetic driving module has to be further provided, rather than only the capacitance type electrode. Accordingly, the number of essential components is increased, and necessary processes have to be increased disadvantageously.
The capacitance-type touch screen in a related art has following disadvantage.
First, the contact area of the sensor panel face of the tip possessed by the stylus pen is relatively small and the mutual capacitance variation (ΔCm) is small. Accordingly, it is difficult to sense the variation of the mutual capacitance in the touch implemented by the stylus pen and the accuracy of the coordination extraction can be deteriorated.
Second, when the tip of the stylus pen is smaller than the electrode provided in the sensor panel for sensing, there could be coordinate distortion according to presence of the electrode, thereby causing sensitivity deterioration of the sensor.
Third, there is a disadvantage of failure in distinguishing the touch implemented by the palm in contact with the electrode in the stylus pen input from the touch implemented by the stylus pen. In other words, it is difficult for the capacitance-type touch screen in the related art to have the function of palm rejection in the touch implemented by the stylus pen.
Fourth, the method for detecting the stylus pen touch according to another driving module that is different from the driving module of the finger touch, for instance, the electromagnetic type driving module is introduced. However, in this instance, an auxiliary panel that can be detected by an auxiliary electromagnetic driving module has to be further provided, rather than the capacitance type electrode. Accordingly, the number of essential components is increased and necessary processes have to be increased disadvantageously.